1. Field of the Invention
The present invention relates generally to a capacitive microelectromechanical switch based on utilization of the Lorentz force.
2. Description of the Related Art
There now exists a small but growing number of microelectromechanical systems (MEMS) including micro-actuators; examples of which are switches, resonant magnetometers, micro mirrors, micro valves, etc. A typical MEMS shunt switch 10, as illustrated in FIG. 1, includes a beam bridge 12 of length L, width w, and thickness t, and a pull-down electrode 14 having a length W and spaced from the beam bridge 12 to form a gap 16 of width g. When a voltage V is applied, the electrostatic force F causing the bridge to deflect toward a substrate 18 is given by the following equation:                     F        =                                                            ɛ                0                            ⁢              Ww                                      2              ⁢              g                                ⁢                                    V              2                        ⁡                          (              N              )                                                          (        I        )            where ε0=8.854×10−12 C2/N−m2, where C is coulombs and N is Newtons. As the gap 16 decreases, the electrostatic force increases. When the deflection is greater than approximately ⅓ of the initial gap 16, this force exceeds the restoring force of the bridge and causes the switch to snap closed. The minimum voltage that causes this to happen (pull-down voltage, Vp) is given by the following equation:                               V          p                =                                                                              8                  ⁢                  k                                                  27                  ⁢                                      ɛ                    0                                    ⁢                  Ww                                            ⁢                              g                3                                              ⁢          V                                    (        II        )            where k is the spring constant.
Accordingly, to actuate a MEMS-based switch having the gap 16 of from 1.5 to 5 micrometers, typically it is required that a pull-down voltage be from 30 to 90 V. In the context of MEMS, these voltages are high enough to create problems associated with energy losses, processing and reliability.
A need therefore exists for a MEMS-based switch actuateable by a relatively low pull-down voltage.